I am using the code below to strip white spaces from my genereated XML, but it is giving me the following error:

**White space cannot be stripped from input documents that have already been loaded**

I am using this code in an XSLT Mediator in SDL Tridion 2013.

<!-- language:lang-xml -->

    <?XsltMediator extensionsTbbId="tcm:1-2-2048"  
                   inputItemName="ComponentXml" 
                   outputitemname="Output"?>
    <xsl:strip-space elements="*" />
    <!-- below comes my XSLT code -->

Please help me, is something wrong with XSLT Transform in 2013 or I am doing some thing wrong?